Human teeth vary in shape in accordance with their position and function, but share a common structure. As seen in FIG. 1, a tooth 10 consists of a central pulp 12 that communicates with arteries 14, veins 16, and nerves 18. This pulp 12 is surrounded by a calcareous substance known as dentin 20.
As also seen in FIG. 1, the teeth project from sockets 22, or alveoli dentalis, in the alveolar bone 31 of the maxillae (upper jaw) or mandible (lower jaw).
Each socket 22 is a depression in the bone of the jaw lined by a connective tissue known as the periodontal membrane 24. The portion of the tooth 10 that actually fits into the socket 22 is formed into one or more roots 26. The root 26 is joined to the periodontal membrane 24 and held into the socket 22 by a calcified connective tissue known as the cementum 28. The periodontal membrane 24 serves as a “shock absorber” during the mastication (chewing) process.
The projecting portion of a tooth 10, known as the crown 11, comprises grinding surfaces and is covered by another calcified connective tissue known as enamel 30.
The gums 32, or gingival tissue, cover the base of the crown 11 and project between adjacent surfaces of the teeth 10. Normal, healthy gum tissue 32 serves to anchor teeth in place, as illustrated in FIG. 2.
Gum disease, or periodontal disease, is an inflammation or infection of the gingival tissue. Periodontal disease is caused by a sticky film of bacteria, called plaque. Over time, plaque hardens into calculus (tartar).
Mild inflammation, characterized by red, swollen, and bleeding gums 32, is known as gingivitis. Poor oral hygiene is the primary cause of gingivitis. This early stage of periodontal disease is reversible with proper professional care and good oral home care.
If left untreated, the disease spreads to other supporting structures including alveolar bone 31, producing a more advanced stage of periodontal disease known as periodontitis.
Periodontitis, illustrated in FIG. 3, results in the destruction of alveolar bone 31 and the periodontal membrane 24. This stage is characterized by the gums 32 receding or pulling away from the teeth, resulting in the formation of pockets between the teeth and gums 32.
As the disease progresses, teeth become loose, often necessitating extraction. Thus, periodontal disease is a major cause of tooth loss.
A variety of conditions have been found to contribute the development and advancement of periodontal disease, including tobacco use, genetics, pregnancy, puberty, stress, medications, clenching or grinding of teeth, diabetes, and poor nutrition.
Because of the widespread nature of the disease, there have been a variety of methods devised to implant and secure a dental prosthesis.
The most common type of implant is endosseous, in which a screw or similar device is inserted beneath the jawbone. The device serves to mimic a root structure and protrudes through the gum to hold a prosthesis.
However, when an endosteal implant is not possible due to minimal bone height, a subperiosteal implant can be placed on top of the jaw with the metal framework's posts protruding through the gum to hold the prosthesis.
A conventional prior art endosteal implant system 100, depicted in FIG. 4, typically comprises an implant 110, an inserting device 120, a closure screw 130, and an abutment 140 adapted to receive a dental prosthesis 150.
Conventional implants 110 are cylindrically-shaped members commonly made of rigid, non-expandable biocompatible materials, e.g., a metallic alloy (e.g., titanium alloy) or ceramic (e.g., Al2O3).
The material can also permit osteo ingrowth (growth of bony tissue), also known as ankylosis, into the implant 110.
The implant 110 may be of a hollow or solid nature. A hollow nature further encourages osteo ingrowth into the implant 110. In either a hollow or solid arrangement, the top portion of the implant 110 protrudes above the gum line and is adapted to receive the closure screw 130 and the abutment 140. The implant 110 may additionally contain holes penetrating the wall of the implant to further promote osteo ingrowth.
The inserting device 120 is a tool adapted to couple the implant 110 and aid in the insertion of the implant 110 within the jawbone 160.
The closure screw 130 is a screw adapted to fit within the top portion of the implant 110. The closure screw 130 serves to cover and protect the top portion of the implant 110 after insertion into the jawbone 160 and prior to attachment of the abutment 140.
The abutment 140 is adapted to fit within the top portion of the implant 110. The abutment 140 serves to permit attachment of a dental prosthesis 150.
In use, the system 110 is employed in a two-part procedure. In the first part of the procedure, the site is prepared for the insertion of the implant 110 by conventional techniques.
As shown in FIG. 5A, the implant 110 is then inserted into a predrilled hole 170 (represented by phantom lines in FIGS. 5A-5D) within the jawbone 160 by using the inserting device 120 to screw (represented by arrow in FIG. 5A) the implant 110 into the jawbone 160 (e.g., with the aid of a ratchet).
The inserted implant 110 is shown in FIG. 5B. Next, as also shown in FIG. 5B, the closure screw 130 is then screwed (represented by arrow in FIG. 5B) into the top portion of the implant 110.
The first part of the procedure is then complete. The second part of the procedure is performed desirably at least several weeks later. This waiting period permits time for osteo (bone) ingrowth into the implant 110. This process however does not reestablish the periodontal membrane/ligament that was destroyed as a result of the tooth loss. The contact between the implant and the bone is a rigid connection with no dampening effect.
After the appropriate waiting period, the second part of the procedure is then performed. First, the closure screw 130 is removed (not shown).
Second, as illustrated in FIG. 5C, the abutment 140 is screwed (represented by arrow in FIG. 5C) into the top portion of the implant 110.
Finally, as shown in FIG. 5D, a conventional dental prosthesis 150 is attached to the abutment 140 using conventional techniques.
As the prior art illustrates, conventional ankylosing implants require the procedure to be at least two-step and require more than one office visit.
Despite their widespread use in prior art for promoting osseointegration, titanium and titanium alloys present certain other challenges to providing an optimal dental implant. Titanium and suitable titanium alloys are orders of magnitude higher in stiffness than human bone, and therefore dental implants formed from such materials transmit most of the forces of mastication. If the implants are cylindrical, the force is predominantly transmitted through the implant to the opposite end, and little or no force is transmitted laterally. Addition of threads can transmit some of the forces of mastication laterally. However, in some cases implants of this design transmit insufficient lateral forces to bone or tissue surrounding the lateral surfaces of the implant and most of the forces are borne by the bone or tissue in-line with the longitudinal or force axis of the implant. This can lead to a phenomenon known as stress shielding of the surrounding bone. Specifically, it has been determined that inadequate stimulation of bone tissue over extended periods causes the bone tissue to be resorbed by the body. This effect becomes apparent when bone surrounding the dental implant is not adequately stimulated due to, for instance, transmission of a majority of forces created during mastication by a stiff dental implant through the implant. The lack of stimulation along of the tissue along the implant can cause saucerization, otherwise known as bone die-back, which progresses around the upper portion of an otherwise healthy dental implant. The loss of bone can lead to destabilization and even loosening of the dental implant. Additionally, once sufficient bone tissue has undergone resorption, portions of the implant body become exposed, and this surface, which is typically textured to provide high surface area, is susceptible to infection.
Therefore, it would be advantageous to design a dental implant able to transmit the forces of mastication to surrounding bone tissue and reduce stress shielding.
Story (U.S. Publication 2001/0000486) describes a dental implant having a force distribution shell to reduce stress shielding. The device according to Story is composed of a metallic core surrounded by a polymeric shell with a modulus of elasticity lower than the metallic core, in order to transfer more of the forces of mastication to surrounding bone tissue. However, Story teaches a cylindrical implant, which may not transfer a sufficient amount of force to prevent stress-shielding. The device as described by Story is a single implant constructed of two materials. This construction does not allow the surgeon to create a significant compression fit that will sustain the initial mastication forces required for immediate loading. The separate component system allows the surgeon to create a very secure compression fit between the implant and surrounding bone tissue that will sustain these immediate load forces.
Thus, there remains a need for a straightforward, cost effective dental implant that can be inserted easily and with a minimal number of procedures or office visits. Further, the need remains for an implant that provides stability, comfort, long-term wear and reduced stress shielding.